Flow regulators are known with two or three ways, being provided with a bi-directional asynchronous motor that, through a gear kinematic motion, produces the linear movement of a shutter; such a shutter operates for closing and opening one or more liquid inlet or outlet ducts, in order to shutter the flow rate: by varying the position of the shutter, it is therefore possible to modify the flow rate of the liquid that flows in a utilizing apparatus being connected to the hydraulic circuit.
Most of the known devices carry out the adjustment of the shutter position in a somewhat approximate way, by operating the motor for a prefixed time, to which a certain position of the shutter corresponds; according to other known solutions, which are more complex from the manufacturing viewpoint, sensors means of the shutter position are provided.
Valves are also known, being provided with a liquid meter; such valves are provided for carrying out the delivery of a prefixed liquid quantity, and then to return to the the normal closure condition, until the next delivery cycle.
A typical problem of the known flow rate adjusters or regulators, and in particular of those being of the type with a time-controlled shutter, is the poor precision, deriving from the absence of a closed-loop control system, as it will be better result in the following.
A further drawback of said flow adjusters is the rapid deterioration of their mechanical parts; such a deterioration is due to the continuous stress to which the shutter kinematic motion is made subject, when the electric supply is still active at the attainment of the end of stroke; such a drawback has been partly reduced by the use of the cited sensors for the shutter position. However, also in these solutions, the maintenance of the shutter in a prefixed position cannot guarantee for itself the attainment of a constant liquid flow rate; in fact, with the same passage section, a liquid flow rate can vary in function of the pressure variations in the relative hydraulic network.
In the case of pressure variations, and therefore of the flow rate, the known systems are therefore not suitable to allow a sufficiently precise adjustment, inasmuch as they are not able to control eventual flow variations, that can depend upon different causes (for instance, restrictions and occasional occlusions of the conduits).
Another drawback, being typical in the sector of application of the present invention, derives from the difficulty of utilizing the same regulator onto different categories of thermal convectors or heat exchangers, i.e. having different passage sections for the liquid; the connection of a regulator having a passage section being greater than the passage section of a given heat exchanger determines in fact the practical impossibility of exploiting all the adjustment range of the regulator.
For example, in the case of a regulator having a passage section being double with respect to the passage section of the conduits of the heat exchanger, the adjustment range being comprised between the "all open" position and "50% open" position of the shutter becomes practically useless and the adjustment of the total flow rate of the liquid may be realized by exploiting only the adjustment of the remaining 50% of the controlled stroke of the shutter; the measure resolution of the device is therefore halved, with the consequent precision loss.
For a more specific example, let consider a regulator, being provided for the use on a heat exchanger or thermal convector having the conduits of a given section. Such a regulator is equipped with a shutter having a total stroke of 8 mm, and with an adjustment system that carries out the measure of the shutter position in 80 points; in this case, we have a resolution of 0,1 mm per point, and therefore a rate adjustment of the flow regulator with steps being equal to 1/80.
Consider now that such a regulator is connected to a convectors with conduits being of smaller section, for example being equal to 1/8 of the previous one; the work range of the regulator is therefore reduced to 1/8(i.e. 1 mm) of the total possible adjustment range (i.e. 8 mm): in this case, always considering a resolution of 0,1 mm per point, we will have therefore a flow rate adjustment with steps of 1/8, which is clearly less precise than the previous one.
From the given example, in which the effective adjustment is equal to 1/8 of the total possible adjustment range, the precision or resolution loss of the systems according to the known art is evident, in the case of use on various conduits having different sections.
The cited drawback involves necessarily a calibration of the work starting point of the regulator, which has to be carried out in the manufacturing phase of the device or during its installation. In the first case, it becomes necessary to produce a wide range of different regulators, each having passage sections being equal to the passage sections of the conduits of the relevant convectors, with evident drawbacks for standardizations, stock management, availability in short time of devices being different, etc.
Concerning the second case, regulators are known which allow, in the installation phase on the utilizing apparatus, for the manual calibration of the work starting point of the shutter; such devices are however easily subject to adjustment errors in the installation phase.
Other problems of the known adjustment devices depend upon the fact that they are realised in a metallic material; this is necessary due to the high clamping forces that, in the installation phase, have to be exercised on the hydraulic terminals of the flow regulator device, for assuring the necessary sealing.
Such a realization causes the formation of condensate onto the metallic walls of the regulator body: the presence of such a condensate, and the same fact that the metallic body is an optimal electric conductor, require therefore great attention in the electric insulation of the device; in particular, a high insulation is required between the electric connector of the actuator and the metallic body of the device.